1. Field of the Invention
The invention relates to non-impact printheads for recording and more particularly to a radiation-emitting printhead having a plurality of recording elements and whose radiation is required to be focussed onto a recording element.
2. Description Relative to the Prior Art
Non-impact printers such as those using light-emitting diodes are well known. In such known printers, one or more extended rows of light-emitting diodes (LED's) are arranged so as to selectively emit light to expose a photosensitive surface to record images. With regard to the recording of images on electrophotographic recording elements such as photoconductive drums, the printheads are required to be placed proximate to the drums. Room must also be provided around the drum for electrostatic chargers, one or more developing stations and transfer devices for transferring images to recording members. In order to provide more compact printers such as those suited for portability and for table top operation, the drum can be made smaller thereby requiring less availability of room for placement of the various members adjacent to the drum surface. The prior art is replete with suggestions for making LED printheads more compact but the suggestions provided by the prior art are far from satisfactory from a manufacturer's point of view in making such printheads. Typically, such printheads in addition to the one or more rows of LED's will include a series of integrated circuit driver chips that are connected to the LED's arranged in a row. The chip arrays may then be assembled end to end to form a single row of several thousand LED's. The driver chips may each include circuitry for receiving data signals and enabling the LED's selectively in accordance with such signals. Each driver chip may be suited for driving one half of the LED's in a chip array so that typically two driver chips are employed for driving a respective chip array of LED's. When these driver chips are mounted to either side of the row of LED chip arrays one group of the driver chips is used to drive odd-numbered LED's and the other group is used to drive even-numbered LED's.
It is preferred from a manufacturing standpoint to mount the driver chips and LED's to a common surface of a support. In one example, it is known to mount three LED chip arrays of say 128 LED's each to a metal or ceramic tile with a corresponding respective number of driver chips for driving even and odd LED's. This assembly forms a module which may be tested and those modules deemed satisfactory may be mounted one after the other upon a printed supporting surface to form the printhead.
One approach noted in the prior art is illustrated in U.S. Pat. No. 4,767,172. In this approach, each LED is centered in a hemispherical cavity in a collector array in order that radiation from the LED enters the collector unrefracted. The collector array includes a convex lens portion and a parabolic reflecting surface portion. Light that exits from the LED that is substantially perpendicular to the substrate supporting the LED is applied to the convex lens and is collimated. Light exiting substantially parallel to the substrate strikes a parabolic reflecting surface at greater than the critical angle and is also collimated. The two concentric collimated beams are combined and applied to a photoreceptor via a light pipe or optical wave guide secured to the collector.
As noted in this patent this recorder is directly used with LED's that form broad light patterns and as such, are used for patch generation and for pitch and edge erasure on the surface of a photoreceptor. In the use of LED's for recording pictorial or alphanumeric images, LED's may be spaced 300 or more to the inch. Providing a lens array as disclosed in the above reference thus represents many difficulties from the manufacturing standpoint.
It is further known, see for example U.S. Pat. No. 4,907,034, to employ a gradient index fiber lens array such as a Selfoc lens, trademark of Nippon Sheet Glass Co., Ltd. to collect light from LED's and focus the light upon a receptor. An advantage of these arrays is that no one particular fiber needs to be registered or aligned with a particular LED. However, the spacing between the LED's and the object side of the lens array needs to be accurately made as well as does spacing between the image side of the array and the surface of the photoreceptor. Any errors in these spacings may be accommodated through the lens depth of focus capability. Light from each LED is collected by groups of fiber and focussed upon the photoreceptor.
Thus, it is an object of the invention to preserve the convenience and desirability of using a gradient index fiber lens array in combination with LED's or other radiation-emitting recording elements in a narrow printhead.
In addition, it is a further object of the invention to preserve the manufacturing convenience of continuing to manufacture LED arrays or other radiation-emitting recording elements and their associated driver chips upon a common surface of a substrate.
It is, therefore, a further object of the present invention to provide a new and improved light collector for radiation from a plurality of recording elements.
Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.